Cabela's and bass pros have all the transducers you could ever want at a OK price.
Look athe transducer and see if the scratches have cracks then let water in, they dont have to be all the way in if there is not enough plastic between the guts and the flat botom every time you put the boat in the water conensation well do the exact thing you described....also check the cable where it goes into the transducer, a broken or cracked cable can let mositure in....Try to find someone who has the same sonar as you and do the swap test...if his does the same on your boat...its about $50 for a new transducer....DJ